The present invention relates to a control device for a robot that operates in an inertial coordinate system, in other words, one that operates in an inertial region such as in space or under the sea where the force of gravity cannot be used. In particular, it relates to a control device for a robot that moves a robot arm to perform a task while free flying in space or under the sea.
With conventional techniques, if a hand of a floating robot arm is to be made to follow a target path in an operating coordinate system (an inertial system), the main body of the robot is forced to move by the reaction force generated by the arm's movement, and this causes a problem in that it is difficult for the hand to accurately follow the path.
A technique of generating velocity instructions by taking into consideration the dynamic behavior of the entire system, including the main body of the robot, has been proposed in "Resolved Motion Rate Control of Space Robotic Manipulators with Generalized Jacobian Matrix", by Umetani and Yoshida, Journal of the Robotics Society of Japan, Vol. 7, No. 4, pp. 63-73, 1989. Since this technique provides velocity control, the problem remains of how to generate target position and orientation instructions, and the method used to generate velocity instructions necessitates massive calculations such as computations of mass characteristics, centers of mass, and inertial tensors for each robot arm, so the technique cannot cope readily with changes in parameters.
Various other techniques have been proposed for controlling movement of the main robot body caused by reaction force, by adding propulsion actuators to the main robot body or by adding torquers that generate torque. These techniques are described in papers such as "On the Dynamics of Manipulators in Space Using the Virtual Manipulator Approach," Z. Vafa and S. Dubowsky, Proc IEEE Int. Conf. on Robotics & Automation, pp. 579-585 (1987), and "Experiments on the Control of a Satellite Manipulator," H. L. Alexander and R. H. Cannon, Proc. Material Handling Research Focus, Georgia Institute of Technology, pp. 1-10 (1986). However, these techniques require some form of propulsion generation means or torquer, so they are not advantageous from the energy-saving point of view.
Other proposed techniques for controlling a robot use sensors in the end of the robot hand to measure a relative position or relative velocity toward an object that the robot hand is to approach, and feed this value back to the robot to control it. Such techniques are described in, for example, "Sensor Feedback Control of Space Manipulators," by Masutani, Miyazaki, and Arimoto, Pre-prints of Fifth Lectures of Robotics Society of Japan, pp. 245-248, 1987. Since these techniques require a target object, and they also require something to act as some sort of verification mark as well, they cannot be used to move a hand of a robot arm in a desired manner in places where there are no surrounding objects.